A patient's inspiratory effort is difficult to determine from conventional measurements of airway pressure, flow, and volume waveforms displayed on a mechanical ventilator providing ventilatory assist to the patient. Thus, the accuracy by which ventilatory assist is delivered to the patient can be jeopardized by such measurements without the situation being noticed by the caregiver.
The main reason for this is that an airway pressure/flow sensor, airway impedance sensor, ultrasound sensor, rib-cage movement sensor or other device that indicates the respiratory direction during unassisted breathing would be affected by mechanical ventilator's assist delivery.
Trans-esophageal measurements of diaphragm electrical activity (EAdi) provide sensitive and accurate determination of neural respiratory drive and are valid to determine patient-ventilator interaction. Techniques for obtaining and using such measurements are described in International Application Publication No. WO 2013/071404 to Sinderby et al., the disclosure of which is incorporated by reference herein in its entirety. However, these techniques use an esophageal catheter inserted in the patient's esophagus, the esophageal catheter comprising EAdi sensors mounted at the level where the esophagus passes through the diaphragm. Although esophageal catheters are frequently used to feed or medicate critically ill patients or to avoid aspiration in such patients, not all patients receive esophageal catheters.
Another method to measure electrical activity of inspiratory muscles uses surface electrodes placed on the neck and/or ribcage of the patient. However, due to the multilayered muscular architecture of the human body, electrical activity/surface electrode (EAse) signals may represent at once activity of inspiratory muscles as well as activity of intercostal muscles that may be activated to alter or maintain body posture of the patient. Surface electrodes will also detect electrical signals from the patient's heart. Conclusively, non-validated EAse signals do not provide sufficient and valid information related to inspiratory effort of a patient.
Therefore, there is a need for non-invasive methods and systems for obtaining validated information related to inspiratory effort of a patient when use of invasive sensors is avoided.